practice

• Star life cycle - stars same size as the sun 


  cloud of dust (nebula) - gas and dust pulled together by gravity

  nuclear fusion begins, when forces are balanced star is stable. expands, cools and becomes red giant

  Red giant - shrinks temperature rises glows much brighter. Becomes white dwarf.
• White Dwarfs - very hot but small. Eventually it will stop shining and become black dwarf
• Star life cycle - bigger than the sun

  Cloud and dust, pulled together by gravity causing temp to increase. protostar.

  Hydrogen nuclei fuse to form helium nuclei

  star becomes main sequence hydrogen begins to run out

  helium nuclei fuse to make a heavier elements

  up to iron. Star expands and becomes red super giant and explodes (supernova). creating elements heavier than iron and distributing them throughout the universe

  leaving neutron star or black hole
• Terminal velocity 


  as the velocity increases air resistance increases. Until air resistance becomes equal to the weight of ... so the resultant force its zero.
• cons of momentum 


  momentum before = momentum after

  before momentum of skateboard is zero

  after jumping skateboarder has momentum forwards so skateboard has equal momentum backwards
• Cons of momentum - stationary object

  momentum is conserved in the collision

  momentum before = momentum after

  momentum of pin increases

  therefore the momentum of the ball must decrease
• Stopping Distance - why will distraction increase stopping distance

  stopping distance = thinking distance + braking distance

  additional time for the driver to apply brakes, (reaction time increases)

  so thinking distance increases
• Refraction - explain 


  different parts of the wavefront enter the glass at different times

  speed is less in glass
• Describe difference between longitudinal and transverse waves

  oscillation for transverse is perpendicular to the direction of energy transfer and longitudinal waves are parallel to the direction of energy transfer.
• Explain how electrical signals in the transmitter product a signal in the receiver 


  electric current

  radio waves are absorbed by receiver inducing electrical current

  at the same frequency
• Electromagnet 


  there is a current in the solenoid

  creating a magnetic field

  attracting the bolt
• explain why the coil rotates when there is a current in the coil - motor effect 


  there is a magnetic field

  current in a wire causes a magnetic field

  current is in opposite directions in each side of coil

  split ring the force on the left/right side is always in the same direction
• Explain how a moving-coil loudspeaker produced a sound wave

  creates a magnetic field

  which interacts with the permanent magnet field

  producing a force causing the coil to move

  direction of the current reverses the direction of the force reverses

  cone vibrates - air particles vibrating
• Generator effect 


  the coil moves through the magnetic field

  a pd is induced

  there is a complete circuit so a current is induced

  direction of the current reverses every half turn
• Microphones 


  sound waves cause the diaphragm to vibrate

  the diagram causes the could to vibrate

  the could noves through the magnetic field

  a pd is induced